1. Field of Invention
The invention relates to a deviation device for a film web and a method for deviating a film web.
2. Description of the Prior Art
Deviation devices of this type are used in plants for sometimes producing a large number of film webs. Such a plant has been described in DE 102 44 869 A1 by way of example. The plant described in the aforementioned document is a so-called blown film extrusion plant, using which tubular film webs can be produced at least initially. These tubular film webs are guided over different deviation devices and later wound up directly in the form of film tubes or first separated into film webs and then wound up. However, such deviation devices are also used in plants used to produce flat films. The components of such flat film extrusion plants have been described in DE 198 23 304 A1. The film webs produced using such plants are also guided over different deviation devices and later wound up. Deviation devices are naturally also used in many other film-producing or film-processing plants and machines.
In deviation devices disclosed in the prior art, deviation elements are used, which operatively interact with the film web. The term “deviate” within the meaning of the invention is also meant to connote a “zero deviation.” This means that the film is not deviated out of its transport plane. In the case of “zero deviation,” a deviation device serves to guide the film web. The deviation elements are frequently in direct contact with the film web. However, deviation devices must also be enabled to guide or divert those film webs, which have at least a touch-sensitive surface. In order to prevent these surfaces from getting damaged or otherwise affected, the film web is guided, at least partly, in a contactless manner over the deviation devices. It has been observed that the concept of building up an air cushion between the deviation element and the film web is very suitable for this purpose. The patent application DE 44 40 647 A1 of the applicant of this patent discloses a deviation element, which is provided with openings or bores, from which a fluid, preferably air, flows out, which is present under excess pressure in the interior of the deviation element. In this way, an air cushion is created between the deviation element and the film web.
One particular problem encountered in the disclosed deviation elements that guide a film web on an air cushion is that it is often not possible to create a uniform air cushion due to the finite number of openings or bores on the deviation element, as a result of which the film could develop folds or come into contact with the deviation element.